feat(files): add per-user file favorites

[zjean]

Summary

• Adds a files_favorites join table (userId, fileId, createdAt) with cascade deletes on both FKs and a composite primary key
• New backend service + 3 controller endpoints: GET /spaces/favorites, POST /spaces/favorite, DELETE /spaces/favorite/:fileId
• isFavorite: boolean included in file browse results via a new withIsFavorite option on browseFiles (EXISTS subquery, same pattern as withHasComments)
• Favorites list is filtered by the user's current space/share access — mirrors getRecentsFromUser pattern
• New Angular favorites module: constants, routes, page component, widget (matches recents styling), FileFavoriteModel
• Star toggle column as first column in the file browser table
• Favorites sidebar menu entry with active-state routing
• POST /spaces/favorite accepts full file context (FavoriteFileDto) and performs a find-or-create on the files table so unindexed filesystem entries (negative inode IDs) can be starred immediately — same pattern as share creation

Database

CREATE TABLE files_favorites (
  userId   BIGINT UNSIGNED NOT NULL REFERENCES users(id) ON DELETE CASCADE,
  fileId   BIGINT UNSIGNED NOT NULL REFERENCES files(id) ON DELETE CASCADE,
  createdAt DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
  PRIMARY KEY (userId, fileId),
  INDEX user_idx (userId),
  INDEX file_idx (fileId)
)

API

Method	Route	Description
GET	/api/app/spaces/favorites	List favorites (filtered by current access)
POST	/api/app/spaces/favorite	Add favorite (find-or-create file record)
DELETE	/api/app/spaces/favorite/:fileId	Remove favorite

Test plan

• Star a personal file → appears in Favorites page, icon filled
• Star a file inside a space → appears in Favorites page with space icon
• Remove a favorite → disappears from Favorites page immediately
• Remove user from a space → space files no longer appear in their Favorites list
• Delete a space or share → cascade removes all related favorites automatically
• Trash a file → does not appear in Favorites list
• Star a brand-new (unindexed) file → gets indexed and starred in one request